The present application relates to nonaqueous electrolyte battery. In particular, it relates to a nonaqueous electrolyte battery capable of suppressing an increase in battery internal pressure safely when the battery internal pressure increases.
In recent years, many portable electronic apparatuses, e.g., a camera-integrated VTR (videotape recorder), a cellular phone, and a laptop computer, have made their debuts, and an achievement of miniaturization and higher functionality thereof is facilitated. Along with the trends, demands for batteries serving as power supplies of the portable electronic apparatuses have expanded sharply. Therefore, in order to realize miniaturization of apparatuses, development of a secondary battery having a large energy density and a large power density has been conducted. As for a battery which meets such demands, a lithium ion secondary battery including a positive electrode produced by using a composite material of lithium and a transition metal and a negative electrode produced by using, for example, a carbon material is most suitable.
Regarding the lithium ion battery, an electrolytic solution and an active material are decomposed through overcharge, internal short-circuit, or the like, gases are generated in the inside of the battery, and a battery internal pressure increases. Consequently, the battery may be deformed or exploded because of this increase in battery internal pressure. Therefore, the battery has a structure in which the gases generated in the battery can be released to the outside of the battery.
FIG. 7A is a perspective view of a battery lid 50 in the related art used in a cylindrical battery. FIG. 7B is a top view of the battery lid 50 in the related art. FIG. 7C is a sectional view of a section taken along a line VIIC-VIIC shown in FIG. 7B of the battery lid 50 in the related art, viewed from a direction indicated by arrows.
The battery lid 50 is in the shape of a hat in which a central portion of a circular plate is substantially uniformly protruded in an axis line direction. The battery lid 50 includes a cylindrical protrusion portion 52 disposed at a central portion and an annular flange-shaped portion 51 disposed in such a way as to surround this protrusion portion 52.
A plurality of opening portions 54 are disposed in a side wall 53 of the protrusion portion 52, while the side wall 53 is in the shape of a cylinder surface. For example, the plurality of opening portions 54 are disposed at regular intervals in the side wall 53 of the protrusion portion 52.
When gases are generated in the inside of the battery, the pressure in the inside of the battery increases. If a pressure difference occurs between the inside and the outside of the battery, as shown in FIG. 7C, gases generated in the inside of the battery flow through the opening portions 54 toward the outside and, thereby, are released. Consequently, a pressure increase in the inside of the battery is avoided.
Japanese Unexamined Patent Application Publication No. 2004-319465 describes a technology in which opening portions are disposed in a battery lid and gases generated in the inside of the battery are released to the outside, as described above.
Furthermore, for example, Japanese Unexamined Utility Model Registration Application Publication No. 63-167669 describes a configuration in which a vent hole is disposed in a battery lid and, in addition, wedge-shaped annular grooves, which are concentric and which have different diameters, are formed oppositely in the battery lid from top and bottom surfaces of the battery lid so as to provide a thin-walled portion in a part of the battery lid.
Regarding the battery according to Japanese Unexamined Utility Model Registration Application Publication No. 63-167669, even when the vent hole disposed in the battery is blocked in the case where the battery internal pressure increases, a part of the battery lid is cut at the thin-walled portion disposed in the battery lid (terminal plate), and the battery lid comes into the state of being chipped. The internal pressure is relieved through this chipped portion and, thereby, breakage of the battery is prevented.